Lab 6 Pre-Lab Exercise:
1. Surface anatomy of the abdomen
Visualization of the position of abdominal viscera is fundamental to a physical examination. Some of these viscera or their parts can be felt by palpating through the abdominal wall. Surface features can be used to establish the positions of deep structures. The following structures can be felt (and sometimes seen) in the abdomen.
Xiphoid process: At the midline and inferior to the sternum (in the epigastric fossa).
Costal margin: Formed by the cartilages of the 7th-10th ribs. The 11th and 12th ribs and their cartilages can also be felt posteriorly. The tip of the 9th costal cartilage produces a step about halfway along the lower rim of the margin near the mid-clavicular line.
Iliac crest: The length of the crest can be felt as far forward as its anterior extremity: the anterior superior iliac spine (ASIS). The tubercle of the crest produces an obvious protuberance, 5 cm behind the spine and forms the widest part of the pelvis.
Pubic crest (symphysis): Extends laterally for 2.5cm from the midline symphysis, the pubic tubercle forms the lateral prominence. The tubercle is in the same vertical plane as the ASIS when standing in the erect position. The inguinal ligament connects the ASIS to the pubic tubercle.
These palpable landmarks can be used to delineate the extent of the abdomen: costal margin above, and pubic tubercle, ASIS and iliac crests below. The costal margin separates the abdominal from the thoracic wall. A line between the ASIS and pubic tubercle marks the position of the inguinal ligament (separating the anterior abdominal wall from the thigh and lower leg). The iliac crests separate the posterolateral abdominal wall from the gluteal region.
2. The anterior abdominal wall
The abdomen can be subdivided into regions by a combination of imaginary horizontal planes and vertical lines.
The mid-clavicular line passes through the midpoint of the clavicle, which lies about 9 cm from the midline. When extended, the line crosses the costal margin just lateral to the tip of the 9th cartilage, and passes through the femoral point, which lies midway between the ASIS and the pubic symphysis.
The anterior axillary line passes through the axillary fold produced by the pectoral muscles.
The mid-axillary line lies midway between the anterior and posterior axillary line and when extended passes through the tubercles of the iliac crest.
The posterior axillary line passes through the fold produced by the teres major and latissimus dorsi.
The abdomen is divided by the transpyloric and transtubercular planes (see below) in combination with the mid-clavicular lines to produce nine regions. These planes separate the abdomen into: 1) three central regions (epigastric, umbilical, pubic), 2) three regions on each side (hypochondrium, flank, groin). Pain from the abdominal part of the forgut is referred to the epigastric region, pain from the midgut is referred to the umbilical region, and pain from the hindgut is referred to the pubic region.
The transpyloric plane lies midway between the upper border of the pubic symphysis and the sternal angle. It lies at the level of the lower part of the body of L1 and the tips of the 9th costal cartilages, approximately one hand’s breadth below the xiphisternal joint.
The subcostal plane is drawn through the lowest parts of the costal margins (the cartilages of the 10th ribs) at the level of the lower part of the body of L3. The umbilicus is normally on a horizontal plane that passes through the disc between L3-L4.
The supracristal plane passes through the highest parts of the iliac crests through the level of L4 spine and body.
The transtubercular plane passes at the level of the spine of L5 is approximately midway between the level of the pubic crest and the transpyloric plane.
3. Muscular structures
The rectus abdominis muscle forms a swelling at the side of the midline extending from the pubis to a horizontal line from the xiphoid to the 5th costochondral joint, just below and medial to the nipple. The surface of the muscle may be marked by tendinous intersections, one at the level of the umbilicus, the second at the level of the xiphoid, and the third midway between these two.
The linea alba is overlaid by the media furrow. It is 1.25 cm wide above the umbilicus but tapers to a narrow band below. The linea semilunaris produces a shallow curving furrow at the side of the rectus. It runs from the pubic tubercle to the tip of the 9th costal cartilage.
External oblique muscle of which the medial aponeurotic portion and the lateral muscular portions meet at the line between the ASIS and the tip of the 9th costal cartilage. The upper border is marked by a line from the xiphoid horizontally to the 5th rib. The short posterior border runs vertically from the tip of the 12th rib. at the lateral edge of the sacrospinalis to the iliac crest. The lower border is the inguinal ligament.